VSP Meshing. Rob McDonald Cal Poly. VSP Workshop

Transcription

1 VSP Meshing Rob McDonald Cal Poly VSP Workshop

2 Paths to Cart3D Quadrilateral Wireframe Export CART3d File (.tri) Unintersected Triangle Wireframe CompGeom Export CART3d File (.tri) CFD Mesh Output.tri Smooth Bezier Surface Cart3D intersect Intersected Triangle Wireframe Triangle Mesh 2

3 Paths to Cart3D Quadrilateral Wireframe Export CART3d File (.tri) Unintersected Triangle Wireframe CompGeom Export CART3d File (.tri) CFD Mesh Output.tri Smooth Bezier Surface Cart3D intersect Intersected Triangle Wireframe Triangle Mesh 3

4 Unintersected Triangle Wireframe Intersected Triangle Wireframe Quadrilateral Wireframe Triangle Mesh 4

5 Pros / Cons of Paths Unintersected CompGeom CFD Mesh Pros Speed Robustness Derivatives with design framework Pros Speed Robustness Special cases Subsurfaces Pros Triangle Quality Special cases Subsurfaces Negative Volume Actuator Disk Cons Robustness Coincident faces Nacelles Extra step Cons Robustness Recommended for Cart3D Today Cons Robustness 5

6 Export Unintersected (before)

7 Export Unintersected (after) 7

8 8

9 Execute CompGeom (before)

10 Execute CompGeom (after) 1 10

11 Export CompGeom

12 Practice Session Unintersected CompGeom Save for Cart3D tutorial Resolution Effects (quads to triangles directly) Num Pts Num XSecs 12

13 CFD Mesh Generator 13

14 CFD Mesh Surface mesh generator Isotropic triangles (no stretching) Smooth Bezier surfaces Bezier intersection curves Subsurfaces Negative volume Actuator disk Sourcing control Curvature control Optional wakes Optional half-models Optional domain modeling Preferred for most CFD tools CBAero Pointwise AFLR3 Fun3D FlightStream TetGen etc. 14

15 Local Radius of Curvature r Greatest Principal Normal Curvature r = 1 k 15

16 Curvature Meshing Criteria Max Gap Num Circle Segments g l l Num Circle Segments = 8 $ & l = % '& r > g; 2 2 r g g 2 r g; 2 g # % l = $ % & N > 2; N 2; r 2 sin( π N ) r 4 N 16

17 Growth Ratio Limiter Growth Ratio X Limits length of next edge to ratio of current edge. 17

18 Rigorous 3D Growth Limiting Off (faster) On (slower) 18

19 Source Types Point Line Box 19

20 Sourcing Attached to components (u, w) Size in model units (length) Sphere of influence (radius) 20

21 Mesh Criteria Precedence Smallest Edge Across Criteria Subject to Constraints Above & Below Sources Max Edge Len Growth Ratio Max Gap Num Circle Segments Min Edge Len 21

22 Turning Mesh Criteria OFF Sometimes it is useful to turn a mesh criteria OFF. Criteria Direction Value Scaled? Max Edge Len large (scaled) Growth Ratio large 10.0 Sources none Max Gap large 10.0 (scaled) Num Circle Segments small Min Edge Len small (scaled) Max = Min will turn OFF Max Gap & Num Circle Segments Sources Max Edge Len Growth Ratio Max Gap Num Circle Segments Min Edge Len 22

23 Meshing Strategy 1. Set Max based on model dimensions Set Min = Max (turning off MG and NCS) No Sources Adjust Max & Min until satisfied (uniform coarsest) 2. Set Min to smaller value Say Min = Max/20 3. Choose MG or NCS as preferred curvature parameter (CP) Set other curvature parameter (OCP) OFF Adjust CP until satisfied Adjust Min as required (are smallest edges small enough?) 4. Adjust OCP (optional) 5. Add mesh sources as required Resolve flow features 23

24 Top Model Constant curvature (constant radius) Increasing curvature (decreasing radius) Extreme curvature (vanishing radius) File on the wiki. 24

25 CFD Mesh GUI 25

26 Global Global & Curvature Meshing Criteria Rigorous Limiting Switch Global Source Adjustment Intersect Subsurfaces Choose Set Mesh Output Go Button 26

27 Display Display Switches Mesh Output Go Button 27

28 Output Multi-Solid STL Switch File Output Switches File Paths File Browser Button Mesh Output Go Button 28

29 Sources Component Chooser Select Surface Source Type Chooser Component Source List Add/Delete Buttons Individual Source Editor Mesh Output Go Button 29

30 Domain Half Mesh Switch Far Field Switch Far Field Mesh Size Far Field Component List Far Field Comp/Box Switch Symmetry Plane Split Far Field Box Controls Mesh Output Go Button 30

31 Domain Modeling 31

32 Symmetry Plane Splitting 32

33 Wakes Wake Length Wake Angle Component Chooser Wake Switch Mesh Output Go Button 33

34 Negative Components Gen Tab Negative Volume 34

35 Negative Pod 35

36 Propulsion Modeling 36

37 Actuator Disk 37

38 Actuator Disk in Duct 38

39 Practice Session CFD Mesh Top model Experiment with meshing parameters Turn all criteria off play with one at a time Follow meshing strategy CFD Mesh Your model Follow meshing strategy 39

40 Command Line / API vsp airplane.vsp3 -script myscript.vspscript!! # -des airplane.des # Apply design file! # vspscript # Batch only executable! // Script to export Unintersected Cart3D tri file! void main() { ExportFile( output.tri, 0, EXPORT_CART3D ); }! // Script to execute CompGeom and export Cart3D tri file! void main() { ComputeCompGeom( 0, false, NO_FILE_TYPE ); ExportFile( output.tri, 0, EXPORT_CART3D ); }! // Script to execute CFDMesh and export Cart3D tri file! void main() { ComputeCFDMesh( 0, EXPORT_CART3D ); }! 40